Insect Transmitted Nematodes

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Insect Transmitted Nematodes

• Filarial worms
• Tissue dwelling parasites
• Order Spirurida
• Transmitted to definitive host through insect
  bite

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Filarial Nematodes

• Tissue-dwelling nematodes (not in digestive
  tract)
• Possess a unique life cycle stage the
  microfilaria - between the egg and J1
• Egg microfilaria J1 J2
  J3 J4 Adult
• these are present in the bloodstream or skin of
  the definitive host.
• Filarial worms utilize arthropods as vectors.

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Lymphatic Filariasis

• Wucheria bancrofti
• Brugia malayi
• Lymphatic filariasis
• 119 million infected
• Elephantiasis
• Manifestation of lymphatic filariasis

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Distribution of Wucheria bancrofti

• Broad equatorial belt
• Africa, Middle East, Southeast Asia, Indo-Pacific
  islands, Parts of Australia and South America

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Habitat

• Adults live in lymphatic ducts.
• Usually near major lymph glands in lower half of
  body
• Release juveniles (microfilariae) into lymph
• Microfilariae carried to blood stream

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Lymphatic System

• Network of vessels that collect fluid that leaks
  out of the blood into tissues (lymph)
• Redirects lymph back into the blood stream

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Adults of Wuchereria bancrofti
Adults occur in the lymphatic vessels
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Wuchereria bancrofti
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Wuchereria bancrofti

• Females release juveniles into lymph
  (ovoviviparous)
• microfilariae swept into blood stream
• Mosquitoes ingest microfilariae with blood meal

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Wuchereria bancrofti

• Penetrate stomach of mosquito
• Develop in thoracic muscles
• Develop into filariform juveniles

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Wuchereria bancrofti

• Migrate to the proboscis
• Injected into human with blood meal
• Mature in lymphatic ducts

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Periodicity

• Microfilariae in peripheral blood at periodic
  intervals
• Wucheria bancrofti
• In peripheral blood between 1000pm-200am
• In blood of deep tissues during the day
• Coincides with feeding time of intermediate hosts

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Microfilariae of Wuchereria bancrofti
Nocturnal periodicity of microfilariae
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Pathogenesis

• Depends on inflammatory and immune response
• Clinical manifestation varies

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Phases of Pathogenesis

• Asymptomatic Phase
• High levels of microfilaremia
• Immune response down regulated
• Sometimes no symptoms and no microfilaremia
• People in endemic areas
• Sometimes lymphatic inflammation and no
  microfilaremia
• Travelers who get infected

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Phases of Pathogenesis

• 2. Inflammatory (Acute) Phase
• Caused by antigens from adult worms
• Inflammation due to bacterial infection
• Adults interfere with lymph flow
• Lymphedema
• Inflammation of lymph channels
• Inflammation of lymph nodes
• Symptoms
• Chills
• Fever
• Swollen and painful lymph nodes
• Swelling of reproductive organs
• Lasts 5-7 days

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Phases of Pathogenesis

• 3. Obstructive (Chronic) Phase
• Lymph ducts become blocked
• Fibrosis of infected areas
• Swelling
• Accumulation of lymph
• Elephantiasis accumulation of lymph in
  extremeties, fibrosis, and thickening of skin.
• Chyluria (lymph in the urine)

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Affected Areas

• Legs
• Scrotum
• Arms
• Brest

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Pathology of Wuchereria bancrofti
Obstructive phase photos
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Impacts

• Rarely fatal
• Disfiguring
• 40 million people
• Disability
• Daily functions
• Sexual disability
• WHO second leading cause of permanent and
  long-term disability in the world (after leprosy)
• Social impacts

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Diagnosis

• Demonstration of microfilariae in blood
• PCR diagnosis

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Microfilariae of Wuchereria bancrofti

• Microfilariae are seen in blood smears and are
  DIAGNOSTIC
• worms are 230-320 µm long

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Treatment

• Diethyl-carbamazine and Ivermectin
• Kills adults and microfilariae
• Edematous limbs
• Pressure bandages
• Surgical removal of elephantoid tissue

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Epidemiology

• Timing
• Takes 6-12 months for females to release
  microfilariae
• Produce microfilariae for 5-10 years
• How do you get infected?
• Bite from infected mosquito

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Brugia malayi
Causes Malayan filariasis   Distribution -
Orient, South Pacific, and Southern Asia to India
overlaps with Wuchereria bancrofti - but does
not occur in Africa or South America
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Brugia malayi
Morphology and life cycle is similar to that of
Wuchereria bancrofti    
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Brugia malayi
Pathology - Adults live in lymphatic vessels of
the arms and legs and cause elephantiasis in
these regions Difference from
Wuchereria?  
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Heartworms (Dirofilaria immitis)
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Heartworms (Dirofilaria immitis)
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Stages of Dirofilaria immitis
Adult male 6-12 inches long Adult female
12-16 inches long Adults coiled in right side
of dog heart
Unsheathed microfilaria in dog blood - DIAGNOSTIC
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Distribution
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Pathology of Dirofilaria immitis

• PATHOLOGY caused by adult worms.
• First signs of infection involve exercise
  intolerance
• due to inadequate blood supply to lungs
• infected dogs cough, have shortness of breath,
  and tire rapidly.
• 2. Eventually the dog suffers congestive heart
  failure- usually after a period of exercise.
•  

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Dirofilaria immitis

• PREVENTION - chemoprophylaxis
• 2 drugs are used ivermectin (in Heartgard) and
  milbemycin oxime (in Sentinel and Interceptor)
• - How taken?
• How does it work?
• How long to treat?

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Human Cases of Dirofilaria immitis

• HUMAN INFECTIONS of Dirofilaria immitis are rare
  (70 cases).
• Larvae are killed by the host reaction and scar
  tissue nodules form in lungs around worms
• Symptoms are coughing and chest pain.
• In only 4 cases were adult worms recovered from
  the human heart. These were found incidentally at
  autopsy and were not related to the death of the
  patient.

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Onchocerca volvulus
Causative agent of Onchocerciasis or River
Blindness DISTRIBUTION Areas of Africa, Arabia,
Guatemala, Mexico, Venezuela and Colombia 
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Life Cycle of Onchocerca volvulus

• Nodules are most common below the waist in
  region of Africa.
• Nodules are on the head and above the waist in
  Central South America.

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Life Cycle of Onchocerca volvulus
1. Adults live in coiled masses encapsulated
under the skin.
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Life Cycle of Onchocerca volvulus
2. Females produce microfilariae - Microfilariae
of Onchocerca NEVER invade the bloodstream.
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Life Cycle of Onchocerca volvulus
3. Microfilariae in the skin are ingested by the
black fly intermediate host, Simulium damnosum,
when a blood meal is taken.
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Simulium
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Life Cycle of Onchocerca volvulus
4. Parasites develop to J3s in the
musculature of the black fly and migrate to the
mouthparts. 5. J3s are inoculated into the skin
when black fly bites. Adults mature in a year
within subcutaneous nodules.
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Adults of Onchocerca volvulus

Microscopic section showing adults and scar
tissue reaction around them forming the nodule
Skin nodule cut open to reveal adults coiled
together
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Microfilariae of Onchocerca volvulus

Unsheathed microfilariae occur in the skin, never
the bloodsteam
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Pathology of Onchocerca volvulus

ADULTS cause onchocercomas Nodules are about ½
-1 inch in diameter. Nodules are relatively
benign and cause only some disfigurement.
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Pathology of Onchocerca volvulus

• MICROFILARIAE cause 3 severe problems. This is
  the only filarial worm in which microfilariae are
  pathogenic!
• 1. Microfilariae in the skin cause
  
  severe dermatitis
• skin becomes thickening,
• discoloration, and cracking.
•  
• leading to secondary bacterial
  infections
•  
• - itching is so severe some people
  
  have committed suicide

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Pathology of Onchocerca volvulus

2. Microfilariae in skin cont - in parts of
Africa, the skin of the scrotum and inguinal area
loses its elasticity causing hanging groin!
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Pathology of Onchocerca volvulus

3. Microfilariae invade the eye   -blindness
occur as microfilariae die in the eye   -
fibrosis causes clouding of cornea and aqueous
and vitreous humors resulting in blindness   -
fibrosis of the eye is a slow development and
most affected persons are adults over 40 years
old!
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Pathology of Onchocerca volvulus

In many parts of Africa, the sighted young are
responsible for leading the older blind adults.
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Diagnosis of Onchocerca volvulus

• Microfilaria in skin snips!
• - snip must be bloodless so as to not to confuse
  with microfilariae that may be circulating in the
  bloodstream.
• (2) Adult worms in excised skin nodule.
•  

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Onchocerca volvulus

 TREATMENT Ivermectin!
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Onchocerca volvulus

• PREVENTION control of intermediate host black
  flies!
• - Larval black flies live in fast moving
  rivers
• After development in water, adults emerge and are
  blood feeders

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Guinea Worm (Dracunculus medinensis)

• Guinea worm (Dracunculus medinensis)
• transmitted by infected copepods in drinking
  water
• larvae move into the body cavity
• female adult migrates to the subcutaneous
  tissue, causes an ulcer/blister, and releases
  eggs through hole when host comes in contact with
  water

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Guinea Worm (Dracunculus medinensis)

• Guinea worm (Dracunculus medinensis)
• traditionally removed by winding the worm around
  a matchstick over the course of several days
• this may be the basis for the Caduceus symbol
  used in the medical field